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  • Organic Chemistry  (29)
  • Saccharomyces cerevisiae  (10)
  • Nitrate reductase  (9)
  • 1990-1994  (47)
  • 1880-1889  (1)
  • 1
    ISSN: 0170-2041
    Keywords: Housane ; Norcaradiene ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Cycloaddition of a Very Reactive Cyanovinylcarbene with Benzene and 3,4-Dichlorocyclobutene. Molecular and Crystal Structure of 2,3-Dichloro-5-(1-cyano-2-methyl-1-propenyl)-5-housanecarbonitrile and 7-(1-Cyano-2-methyl-1-propenyl)-7-norcaradienecarbonitrileThe cyanovinylcarbene 2 has been generated by photolysis of 3,3-dimethyl-3H-pyrazole-4,5-dicarbonitril (1) and the cycloaddition products with benzene and with 3,4-dichlorocyclobutene have been isolated. The molecular structures of the cycloaddition products 7-(1-cyano-2-methyl-1-propenyl)-7-norcaradienecarbonitrile (3) and 2,3-dichloro-5-(1-cyano-2-methyl-1-propenyl)-5-housanecarbonitrile (4) were determined by X-ray analyses. The bridging bond of the bicyclo[2.1.0]pentane group in 4 is shortened to 1.515 Å by the electronic interaction of this group with the cyano substituent. The vinyl substituent has no influence because of perpendicular orientation.
    Additional Material: 2 Ill.
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  • 2
    ISSN: 1617-4623
    Keywords: Saccharomyces cerevisiae ; Cell cycle ; Proline ; DNA sequencing
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary We report here the isolation of temperature-sensitive mutants of the yeast Saccharomyces cerevisiae which exhibit cdc phenotypes. The recessive mutations defined four complementation groups, named ore1, ore2, ore3 and ore4. At the non-permissive temperature, strains bearing these mutations arrested in the G1 phase of the cell cycle. The wild-type allele of the gene altered in ore2 mutants was cloned. The nucleotide sequence of a fragment which can complement the mutation showed the presence of an open reading frame capable of encoding a protein with 286 amino acid residues. The deduced amino acid sequence showed 25% identity with that of the Escherichia coli Δ1-pyrroline-5-carboxylate reductase, an enzyme of the pathway for the biosynthesis of proline. The ore2 mutants, correspondingly, were found to be capable of growing at the non-permissive temperature on a synthetic medium supplemented with proline. In addition, the chromosomal location of the gene and its restriction map were compatible with those previously reported for the PRO3 gene which encodes the S. cerevisiae Δ1-pyrroline-5-carboxylate reductase.
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  • 3
    ISSN: 1617-4623
    Keywords: Nitrate reductase ; Reporter gene ; Nicotiana tabacum ; Nicotiana plumbaginifolia ; Transgenic plant
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Reporter gene techniques and mutant analysis were used to identify the molecular basis of the regulation of the expression of nitrate reductase (NR) by nitrate and nitrate-, or ammonium-derived metabolites (N-metabolites), in the true diploïd species Nicotiana plumbaginifolia and in the amphidiploïd species Nicotiana tabacum. The N. plumbaginifolia mutant E23 results from the insertion of a Tnt1-like retrotransposon (Tnp2) in the first exon of the single-copy nia gene, which encodes nitrate reductase. One of the resulting transcripts ends in the 5′ LTR (long terminal repeat) sequence of this retrotransposon, and another one in the 3′ LTR. Nitrate and N-metabolites modulate the expression of these truncated transcripts, indicating that intron splicing and termination processes are not essential to these regulatory events. A GUS reporter sequence was transcriptionally linked to the promoter of the nia-1 gene of N. tabacum. This fusion was functional in transient expression assays done with protoplasts derived from mesophyll cells of N. tabacum. However none of the regulatory mechanisms known to affect steady-state levels of the nia-1 transcript were operative under these experimental conditions. Transgenic plants carrying either this fusion or translational fusions of GUS linked to the promoter of either the nia-1 or nia-2 gene of N. tabacum were obtained by Agrobacterium-mediated transfer. A low proportion of the transgenic plants (22 out of 105 independent transformants) expressed GUS activity although at a low level. Only 4 plants exhibited a detectable level of GUS mRNA. The concentration of this mRNA increased significantly in an NR-deficient background, indicating regulation by N-metabolites. Only 2 plants, however, showed regulation (induction) by nitrate. Attempts to use aux2 or nptII reporter sequences linked to either the nia-1 or nia-2 promoter as marker genes for the selection of regulatory mutants of the nitrate assimilation pathway were unsuccessful because of our inability to isolate transgenic plants in which these reporter genes were properly regulated by nitrate. The implications of these results are discussed.
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  • 4
    ISSN: 1617-4623
    Keywords: Nicotiana plumbaginifolia ; Nicotiana tabacum ; GATA-binding factor ; Nitrate reductase ; PCR
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract In higher plants, the expression of the nitrate assimilation pathway is highly regulated. Although the molecular mechanisms involved in this regulation are currently being elucidated, very little is known about the trans-acting factors that allow expression of the nitrate and nitrite reductase genes which code for the first enzymes in the pathway. In the fungus Neurospora crassa, nit-2, the major nitrogen regulatory gene, activates the expression of unlinked structural genes that specify nitrogen-catabolic enzymes during conditions of nitrogen limitation. The nit-2 gene encodes a regulatory protein containing a single zinc finger motif defined by the C-X2-CX17-C-X2-C sequence. This DNA-binding domain recognizes the promoter region of N. crassa nitrogen-related genes and fragments derived from the tomato nia gene promoter. The observed specificity of the binding suggests the existence of a NIT2-like homolog in higher plants. PCR and cross-hybridization techniques were used to isolate, respectively, a partial cDNA from Nicotiana plumbaginifolia and a full-length cDNA from Nicotiana tabacum. These clones encode a NIT2-like protein (named NTL1 for nit-2-like), characterized by a single zinc finger domain, defined by the C-X2-C-X18-C-X2-C amino acids, and associated with a basic region. The amino acid sequence of NTL1 is 60% homologous to the NIT2 sequence in the zinc finger domain. The Ntl1 gene is present as a unique copy in the diploid N. plumbaginifolia species. The characteristics of Ntl1 gene expression are compatible with those of a regulator of the nitrate assimilation pathway, namely weak nitrate inducibility and regulation by light.
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  • 5
    ISSN: 0749-503X
    Keywords: RVS161 gene ; Saccharomyces cerevisiae ; stationary phase entry ; viability loss ; Life and Medical Sciences ; Genetics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology
    Notes: In yeast, nutrient starvation leads to entry into stationary phase. Mutants that do not respond properly to starvation conditons have been isolated in Saccharomyces cerevisiae. Among them the rvs161 mutant (RVS for Reduced Viability upon Starvation) is sensitive to carbon, nitrogen and sulphur starvation. When these nutrients are depleted in the medium, mutant cells show cellular viability loss with morphological changes. The mutation rvs161-1 is very pleiotropic, and besides the defects in stationary phase entry, the mutant strain presents other alterations: sensitivity to high salt concentrations, hypersensitivity to amino acid analogs, no growth on lactate or acetate medium. The addition of salts or amino acid analogs leads to the same morphological defects observed in starved cells, suggesting that the gene could be implicated mainly in the control of cellular viability. The gene RVS161 was cloned; it codes for a 30,252 daltons protein. No homology was detected with the proteins contained in the databases. Moreover, Southern analysis revealed the presence of other sequences homologous to the RVS161 gene in the yeast genome.
    Additional Material: 6 Ill.
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  • 6
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Yeast 9 (1993), S. 495-506 
    ISSN: 0749-503X
    Keywords: Nuclear migration ; protein repeats ; cell cycle ; Saccharomyces cerevisiae ; nutrient starvation ; Life and Medical Sciences ; Genetics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology
    Notes: We have isolated a mutant (rvs272) of the yeast (Saccharomyces cerevisiae) that displays an altered phenotype in stationary phase. It shows a high proportion of large-budded cells with two non-segregated nuclei staying in the mother cell. This phenotype is also expressed in various conditions when cells are synchronized, energy depleted or treated with the antimitotic drug benomyl. The RVS272 gene has been identified as the NUM1 gene already described. This gene presents a 192 bp tandemly repeated motif and we show that the number of repeats can vary from 1 to about 24 among different strains, without apparently affecting the function of the encoded protein. We suggest that this protein could be involved in polymerization catalysis and/or stabilization of microtubules.
    Additional Material: 8 Ill.
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  • 7
    ISSN: 0749-503X
    Keywords: Chromosome III ; Saccharomyces cerevisiae ; mating type ; HML ; BUD5 ; Life and Medical Sciences ; Genetics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology
    Notes: This paper reports the DNA sequence of a segment of 9·8 kb of the chromosome III. The sequenced DNA contains the MATα locus. The new sequence of the MATα locus differs from the previously reported sequence by six modifications in the W segment. We have found the same modifications in the HML locus. The corrected sequence contains, in HML, an open reading frame (ORF) of 190 codons which ends at the border between the W segment and the flanking DNA. In the MAT locus, this ORF extends in the flanking DNA up to 538 codons. This ORF corresponds to a gene independently identified as BUD5 (Chant et al., 1991). This gene presents homologies with the exchange factors SDC25 and CDC25. A large ORF of 1399 codons is found on the opposite side of MATα (toward the telomere). This ORF corresponds to a new gene YCR724. Next to this gene is a small ORF, YCR725, of 127 codons. The localization of this fragment on chromosome III, originally supposed to be distal from the MAT locus based on genetic distance, illustrates variation in recombination frequency along the chromosome and suggests the existence of hot spots of recombination between MAT and the THR4 locus.
    Additional Material: 5 Ill.
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  • 8
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    ISSN: 0021-8383
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 9
    ISSN: 1617-4623
    Keywords: Saccharomyces cerevisiae ; Translation ; Splicing ; Paromomycin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The MSS51 gene product has been previously shown to be involved in the splicing of the mitochondrial pre-mRNA of cytochrome oxidase subunit I (COX1). We show here that it is specifically required for the translation of the COX1 mRNA. Furthermore, the paromomycin-resistance mutation (P inf454 supR ) which affects the 15 S mitoribosomal RNA, interferes, directly or indirectly, with the action of the MSS51 gene product. Possible roles of the MSS51 protein on the excision of COX1 introns are discussed.
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  • 10
    ISSN: 1617-4623
    Keywords: Nicotiana tabacum ; Nitrate reductase ; Retrotransposon ; Transcription
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The effects of Tntl retrotransposon insertion on nitrate reductase (NR) gene transcription have been analyzed in three NR-deficient insertional, mutants of Nicotiana tabacum. In the three mutants, named h9-Nia4, h9-Nia5 and h9-Nia6, Tnt1 was inserted into exon 3, exon 2 and exon 1 of the nia2 NR alloallelle, respectively. The mutants h9-Nia4 and h9-Nia6, which contained Tnt1 insertions that were oriented opposite to the direction of nia2 gene transcription, expressed chimaeric nia2-Tnt1 RNAs, respectively 12 kb and 10 kb long. The size observed in h9-Nia6 was close to the expected size for a full-length hybrid transcript starting and ending under the control of nia2 signals (about 9 kb). The larger transcript found in h9-Nia4 was shown to be due to a failure to splice the nia2 intron 2. The mutant h9-Nia5, which contained a Tntl insertion oriented in parallel with the direction of nia2 transcription expressed two truncated nia2-Tnt1 RNAs, 2 kb and 6.7 kb long. These transcripts arose from termination in the long terminal repeats (LTRs) of Tull. Since no full-length hybrid RNA was detected, we suggest that Tnt1 carries efficient termination signals, which are more efficiently recognized in the 3′ LTR than in the 5′ LTR.
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